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March 27, 2012 (Chicago) -- Sleeping less than six hours a night may make you more likely to have a heart attack, stroke, or heart failure.

A new study puts numbers on that risk. The study, based on more than 3,000 people older than 45, shows that people who sleep less than six hours per night are about twice as likely to have a stroke or heart attack as people who get six to eight hours of sleep. And they are about 70% more likely to have congestive heart failure.

"The optimal sleep time appears to be six to eight hours,” says Rohit R. Arora, MD, chairman of cardiology at Chicago Medical School.

The new study, presented in Chicago at the American College of Cardiology's annual meeting, isn't the first study to link sleep and heart health. But it's one of the largest surveys to do that, Arora says.

That means a lot of Americans could be at greater risk for heart trouble because of their sleep habits. Nearly 30% of U.S. adults report sleeping no more than six hours per night, according to a national health survey.

Exactly how sleep affects the heart is not clear. Arora says he doubts not sleeping enough directly causes heart disease.

But there is evidence that not sleeping enough may ramp up the "fight or flight" response to stress, releasing hormones that speed up heart rate and raise blood pressure. If that happens chronically, it could take a toll.

Or, people could have other medical conditions, such as diabetes, that prevent them from sleeping through the night, Arora says.

Study Details

In the study, people were asked how long they slept each night and if they had ever been told they had congestive heart failure, heart attack, coronary artery disease, angina, or stroke.

Among the findings:

Heart attack: More than 10% of people who slept less than six hours had had a heart attack vs. about 5% who slept six to eight hours.

Stroke: More than 9% of people who slept less than six hours had a stroke vs. nearly 5% who slept six to eight hours.

Heart failure: More than 7% of people who slept less than six hours had heart failure vs. 4.5% who slept more than eight hours.

Sleeping too much may also be an issue. The study's findings show that people who sleep more than eight hours a night may be more likely to have the chest pain of angina and coronary artery disease, a narrowing of the blood vessels that supply blood and oxygen to the heart.

The researchers considered other factors that affect heart health, including age, gender, cholesterol, and blood pressure.

But they didn't consider sleep quality, says JoAnne Foody, MD, a heart specialist at Harvard Medical School and head of the ACC's patient site.

"Poor sleep quality is associated with a number of heart conditions. If you don't get deep sleep -- so-called REM sleep -- the body doesn't have the opportunity to bring blood pressure down. Poor sleep is also linked to obesity, which drives cardiovascular disease," she tells WebMD.

What is clear, Foody and Arora say, is that you need to talk to your doctor if you have trouble sleeping.

"It's not just a matter of being tired; there are lots of potential health consequences. And there's a lot we can do to help you," Foody says.

These findings were presented at a medical conference. They should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.